The present invention is directed toward fins on a watercraft propulsion unit to enhance operation of the watercraft during acceleration and at speed.
During acceleration of a boat of the type and size used in towing water skiers or like recreational purposes, it is common for the craft to assume a bow high attitude when starting which hinders the operator's forward vision. A bow high attitude is also undesirable in that it slows the rate of acceleration.
In recreational boating it is common to utilize a boat for both the towing of skiers, inner tube riders, etc., and for fishing. Such boats are frequently equipped with a trolling plate unit on an outdrive or the lower unit of an outboard motor. Trolling plates serve to reduce propeller efficiency or other propulsion unit to lower boat speed which, in view of engine size, could not otherwise be achieved. For high speeds, such as for water skiing, the trolling plate is retracted to a raised, horizontal position. When so raised, a trolling plate is typically located in a plane above a plane containing the anti-cavitation plate of the propulsion unit.
Prior art includes various types of hydrofoils such as that disclosed in U.S. Pat. No. 5,178,089 wherein the hydrofoil is attached to a lower unit of an outboard motor and has an upturned leading edge and a downturned trailing edge.
U.S. Pat. No. 5,203,275 shows a plate attached to a propulsion unit anti-cavitation plate and having a downturned trailing tab and shaped to abut the rearward surface of the lower housing of a propulsion unit.
U.S. Pat. No. 5,127,353 shows a combination trolling plate and hydrofoil with the hydrofoil attached to the anti-cavitation plate of an outboard motor or stern drive unit and shaped so as to be in abutment with the drive housing.
U.S. Pat. No. 5,493,990 issued to the present inventor discloses a combination including a hydrofoil and a trolling plate unit having an internal latch mechanism.